Abstract: Accompanied by the rapid development of the electronics industry, the demand for decabromodiphenyl ethane (DBDPE) in China has increased rapidly in recent years, and the environmental pollution and toxic effects brought by the wide application of DBDPE have attracted much attention. Activated sodium persulfate (Na₂S₂O₈) was used to degrade DBDPE in sediments, and the degradation dynamics of DBDPE in thermally activated and thermoalkaline composite activation systems were investigated. The optimal degradation conditions were screened, and the mechanism of DBDPE degradation was revealed through the identification of reactive free radicals. Increasing the reaction temperature and initial alkalinity could improve the degradation efficiency of DBDPE. Still, the effect of elevated temperature activation was not as significant as that of adjusting the alkalinity of the system, while Cl⁻ and weak acidity had a significant inhibitory effect on the degradation of DBDPE. The free radicals in the system that degraded DBDPE included HO· and SO₄⁻·radicals, with HO· radicals playing a dominant role in the degradation process of DBDPE. Gas chromatography-electron capture negative chemical ion source-mass spectrometry method (GC-ECNI-MS) showed that there were seven possible products in the oxidative removal of DBDPE by Na₂S₂O₈ and some oxygenated products with less bromine were generated.